BACKGROUND To determine carboxyhemoglobin levels and to investigate carbon monoxide poisoning risk in children. METHODS We determine carboxyhemoglobin blood levels by cooximetry in 65 children, between 15 days and 15 years attended in a pediatric emergency section. We analyze carbon monoxide risk factors (type of heating and smokers in the family). RESULTS Mean carboxyhemoglobin levels in 59 children without acute intoxication was 0.5 +/- 0.87% (range 0-3.8%). There are no significant differences with respect to age and sex. Children with wood or coal heating (0.88 +/- 1.34%) and gas heating (0.58 +/- 0.97%) have carboxyhemoglobin levels higher than children with electric heating (0.28 +/- 0.4%) but differences were no statistically significant. Four patients have carboxyhemoglobin levels > 2%, two with coal or wood hating and two with gas heating. Children with smokers in the family have carboxyhemoglobin levels higher than the rest of children (0.65 +/- 1.05% versus 0.34 +/- 0.45%) without statistical significance. The four children with carboxyhemoglobin levels > 2% live with smokers. Six children suffered carbon monoxide poisoning with carboxyhemoglobin levels between 20.6 and 36.6%. CONCLUSIONS Mean carboxyhemoglobin levels in children are low. There are carbon monoxide poisoning risk factors (wood, coal or gas heating at home, and smokers in the family) in a high percentage of the children, although they did not show statistical significance.